The present invention described herein relates to the materials and devices whose electrical resistance changes in the presence of a magnetic field. More specifically, the invention relates to magnetic sensors and magnetic recording media employing magnetoresistive material.
Considerable effort over an extended time period has been expended in developing new sensors that employ the property of magnetoresistance, that is electrical resistance changes due to the application of magnetic fields. The most widely used material is permalloy which is an alloy of approximately 80% nickel and 20% iron. Permalloy's resistance changes only a few percent in a magnetic field. The fact that the magnetoresistive effect is so small places undesirable constraints on magnetic recording and other technologies employing magnetic field sensors. It would be desirable, therefore, to provide a magnetoresistive material whose resistance changes more than only a few percent in the presence of a magnetic field.
Another type of material has been discussed for its magnetoresistance properties is a multilayer material comprised of superimposed layers of iron, chromium, and iron. See Barthelemy et al. J. Appl. Phys. 67 (9), 5908 (May 1, 1990). The change in the magnetic state due to the application of a magnetic field changes the conduction by as much as 10% at room temperature.
A magnetoresistive material produced by physically mixing iron particles into a rubber matrix has also been produced. However, because simple mixing is employed, the small gaps required for tunneling cannot be obtained. Because rubber is a moderate conductor, it is apparent that the magnetoresistive properties of this material arise from the magnetically induced change in the distance between the iron particles altering the conventional resistance between the particles. This effect is entirely different from the resistance changes due to quantum tunneling in the magnetoresistive material according to the present invention.